1. Field of the Invention
This invention relates to a method of manually feeding a coordinate system on which an operation of an industrial robot (hereinafter briefly referred to as robot) is based, and to a robot control device. More particularly, the present invention relates to a method of manually feeding a position of the origin or an attitude of a preset user coordinate system in accordance with user's requirements, and to a robot control device including a modifying function which is carried out by manually feeding the user coordinate system.
2. Description of the Related Art
Various types of coordinate systems are typically set in a robot control device to control a robot, and can be classified into the following two general categories.
A) Coordinate systems inherent in the robot PA0 a1) World coordinate system defined on the basis of a position which is not varied depending upon an attitude of the robot, and PA0 a2) Face plate coordinate system set on a face plate surface of an arm distal end forming a mechanical interface of the robot. PA0 B) Coordinate systems set by the user with reference to the robot PA0 b1) User coordinate system set on the basis of the world coordinate system so as to provide at least one of constant translation and constant rotation on the world coordinate system, and a typical user coordinate system being referred to as work coordinate system which is set, for example, on a workpiece so as to establish particular relationships with a position or an attitude of the workpiece as an object of robot working, and PA0 b2) Tool coordinate system set on the basis of the face plate coordinate system to show a relative position and a relative attitude (translation and rotation) of a tool distal end point, and the tool distal end point being recognized depending upon the coordinate system during control of the robot.
The coordinate systems can not basically be modified by a user, and include the following coordinate systems:
The coordinate systems include the following coordinate systems:
In these coordinate systems, the user coordinate system, in particular, the work coordinate system is essential to perform a smooth robot operation, and setting accuracy thereof serves as an important factor to affect accuracy of the robot operation. The work coordinate system is typically set and used when, for example, the robot should be operated along a specific line corresponding to an edge or the like of a workpiece. Therefore, it is necessary to set the work coordinate system so as to meet conditions in which, for example, the line agrees with one of the coordinate axes, and the origin agrees with a specific position of the workpiece. Further, when importance is given to the attitude of the robot with respect to the workpiece, a specific relationship is required regarding the attitude of the work coordinate system with respect to the workpiece (for example, a relationship in which three orthogonal edge lines of the workpiece respectively agree with an X axis, a Y axis, and a Z axis of the work coordinate system).
However, it is extremely hard to set the work coordinate system by only one setting operation so as to meet the above conditions. That is, in a general setting operation, a coordinate system that agrees with the desired coordinate system as close as possible can be set by repeating coordinate system setting operations and subsequent observations of the locus of robot movement conforming to the set coordinate system (for example, the locus of movement along the X, Y, and Z axes), many times on the trial-and-error basis.
Further, after the work coordinate system has been correctly set once, a mounting position of the workpiece as machining target is frequently modified and finely controlled. Consequently, the work coordinate system should be modified for each modification or fine control. In the prior art, there is only one way to modify the work coordinate system (i.e., the user coordinate system in general) by resetting of the coordinate system. The resetting operation of the coordinate system is carried out by directly inputting calculated values, imaged values, or measured values about coordinates in a space obtained by moving and/or rotating the world coordinate system by a certain amount, or by teaching a point on an axis (for example, an X axial direction) of the coordinate system, instead of inputting a value as in the case of other values to be inputted.
As set forth above, in the conventional modification of the user coordinate system by the resetting operation, other preset coordinate systems are not effectively utilized, resulting in high loss in view of both an operation time and the accuracy. In addition, since no coordinate system exists in a visible form in a space, it is extremely difficult to set a new coordinate system while holding an image of the coordinate system before the modification.
Even if the image can be obtained, a highly skilled operator is required to accurately and rapidly carry out specific operation according to the image (for example, a corrective operation in which the original coordinate system is moved by a certain distance L in the X axial direction, and is rotated about the Y axis in a normal direction by a certain angle .phi.), in order to set a user coordinate system which is actually fit for the purpose.